In the mid-Qing Dynasty, in order to improve the quality of shochu, Shi Jing shochu workshop underwent technical transformation. Used as a cooler when steaming wine, it is called tin pot, also known as sky pot. When steaming wine, the distilled wine vapor put into the tin can for the first time, the "wine head" cooled by cold water and the "wine tail" cooled by cold water put into the tin can for the third time should be put forward for other treatment. Because the wine cooled in the first pot and the third pot contains many substances with low boiling point and boiling point, only the wine cooled by cold water put into the iron pot for the second time can be picked up, so it is called "Erguotou". This is a very pure wine and the best quality wine. At present, the methods of "pinching the head and removing the tail" and "taking wine by quality" adopted by liquor factories all over the world are based on the technological principle of "Erguotou". At the end of Qing dynasty, the technology of Erguotou had spread all over Beijing and was highly praised by scholars. Wu Yanqi praised in his poem, "People have hated it for thousands of years since ancient times and are willing to be Erguotou so far." Compare Erguotou to "sweet".